Rivers

Question 1

Is the hydrological cycle an open system and why

Answer 1

No, because new water is never added to the earth or its atmosphere, nor is water ever removed

Question 2

How does the water cycle work

Answer 2

• Energy from the Sun heats the surface of the Earth
• Water is evaporated from oceans, rivers, lakes, etc
• The warm, moist air rises because it is less dense
• Condensation occurs when water vapour is turned back into water droplets as it cools down
• Precipitation occurs as water droplets get bigger and heavier they begin to fall as rain, snow and sleet, etc

Question 3

What are the processes in the water cycle

Answer 3

Evaporation
Condensation
Precipitation
Surface run off
Percolation/Infiltration
Groundwater flow
Transpiration

Question 4

What is a drainage basin

Answer 4

Area of land where precipitation collects and drains into any body of water

Question 5

What are the parts of a drainage basin

Answer 5

Mouth
Source
Watershed
Main river channel
Tributary
Confluence

Question 6

Is a drainage basin part of an open system and why

Answer 6

Yes, water that enters as input from precipitation flows out of the system as output of water into the sea and evaporation of water into the atmosphere

Question 7

What are River processes and what do they do

Answer 7

Shape the land in many ways as the river moves from its source to its mouth. Erosion, transportation and deposition contribute to this

Question 8

What is River discharge

Answer 8

Total volume of water flowing through at any given point and is measured in cubic metres per second

Question 9

What are 3 factors affecting work carried out by a river

Answer 9

• Velocity/energy
• Volume
• Bedrock

Question 10

What are 4 main types of river erosion and explain them

Answer 10

Hydraulic action- Force of the river against the banks can cause air to be trapped in cracks and crevices. Pressure then weakens the banks and gradually wears it away
Abrasion- Rocks carried along by the river wear down the river bed and banks
Attrition - rocks being carried by the river knock each other and break into smaller, smoother and rounder particles
Solution - soluble particles are dissolved into the river

Question 11

What are 4 river transport processes

Answer 11

Solution- Minerals are dissolved in the water & carried in solution
Suspension- Fine light material is carried along in the water
Saltation- Small pebbles & stones are bounced along the river bed
Traction- Large boulders and rocks are rolled along the river bed

Question 12

What is deposition, where can it happen, and what can deposition at the mouth of the river create

Answer 12

When a river loses energy, it will drop or deposit some of the material it is carrying
Deposition may take place when a river enters an area of shallow water or when the volume of water decreases- for example, after a flood or during times of drought
Deposition is common towards the mouth
Deposition at the mouth of a river can form deltas, eg: the Mississippi Delta

Question 13

Characteristics and processes in upper valley

Answer 13

Vertical erosion with hydraulic action, abrasion and attrition as dominant processes
Traction and saltation at high flow
Load size is large and angular
V shaped valleys

Question 14

Characteristics and processes in middle reaches

Answer 14

Channel is deeper and wider
Vertical erosion decreasing in importance, more lateral erosion and deposition
Suspension is the main transportation type
Load becomes smaller and less angular

Question 15

Characteristics and processes in lower reaches

Answer 15

Channel is at its deepest and widest, may be tidal
More deposition than erosion
Fine material deposited
Large amount of load but the size is very small and very rounded

Question 16

How are V-shaped valleys and Interlocking spurs formed

Answer 16

In upper course, river is fast flowing but there is little water and load. The river/stream does not have erosive power to remove the hillsides so it makes its way around hills forming Interlocking spurs.
The stream erodes downwards and forms V-Shaped valleys

Question 17

How are waterfalls and gorges formed

Answer 17

Water flows where hard rock lies over soft rock
Water erodes soft rock more easily undercutting the hard rock
Overhang is formed
Overhang collapses eventually
Plungepool develops
Waterfall retreats upstream
Steep gorge like valleys are formed

Question 18

How are potholes formed

Answer 18

Boulders broken off by erosion that sit on the river bed create swirling current

Question 19

How is a meanders formed

Answer 19

In middle course, river has more energy and a high volume of water.
river erodes laterally, to right side and then to the left side, it forms large bends, and then horseshoe-like loops called meanders
Formation of meanders is due to deposition and erosion
FOrce of water erodes and undercuts the river bank on the outside of the bend where water flow has the most energy due to decreased friction
On the inside of the bend, river flow is slower, material is deposited as there is more friction

Question 20

How is an oxbow lake formed

Answer 20

The gap between the arms of the rivers narrowed by erosion
river breaks through narrow gap when high rainfall and flooding occurs
Current along straighter path becomes dominant
Old path of river now dry and an oxbow lake remains

Question 21

How is a floodplain formed

Answer 21

• Area of alluvial deposits
• Valley is eroded to create a wide valley floor
• Deposits layers of alluvial material on the slip off slopes building up into a large flood plain

Question 22

How is a Levee formed

Answer 22

During flood the thickest and coarsest sediments deposited at channel edges
Thin and fine sediments deposited over outer parts of floodplain
natural levees built up after many floods

Question 23

How is a delta formed

Answer 23

When river meets the sea its velocity suddenly reduces
Reduction in velocity means the the rivers load is deposited at the mouth of the river
If the river deposits quicker than the sea can erode then a delta starts to develop

Question 24

What is lag time

Answer 24

The delay between peak rainfall and peak discharge

Question 25

What is shown on a storm hydrograph and how can that change

Answer 25

The discharge of a river is shown on a graph called a flood or storm hydrograph. It shows the rainfall amount and then the discharge of the river. Most of the rain falls onto the land rather than directly into the river. The water then will make its way into the river and you can use a hydrograph to see how quickly this occurs.
Different catchment areas will have different flood hydrographs. Some, with steep slopes and little vegetation, will rise very quickly, and can be described as a “flashy river”.

Question 26

What are some factors that affect river regime

Answer 26

Vegetation and land use
Rainfall
Climate
Shape of land, gradient of slope
Soil type and depth
Type of bedrock
Size and shape of river basin